Orifice fitting mechanisms are useful in measuring the flow of fluid products, particularly gaseous materials such as natural gas in pipelines. The fluid flows across a restricted orifice placed in the pipeline and develops a pressure differential existing across the orifice which is detected and utilized in conjunction with other factors such as pressure, type of fluid, temperature, etc., in order to arrive at a measurement representing the volume of the flowing fluid. This basic principle of flow measurement has been well known for an extended period of time.
In order to provide an orifice fitting mechanism having the capability of removing and installing an orifice plate without shutting down the flow line, an initial orifice fitting development was made by Mr. Paul P. Daniel, resulting in U.S. Pat. No. 1,965,826. Another Daniel U.S. Pat. No. 1,996,192 also discloses an orifice fitting mechanism of this general nature. Further, a more up-to-date orifice fitting design is exemplified by U.S. Pat. Nos. 2,688,987 of Whalen, and 4,286,364 of Connolly.
In the orifice fitting mechanisms set forth above, the orifice plate is mounted in a generally rectangular framework and this framework is moved linearly within the orifice fitting between a body chamber intersecting the flow passages and an access chamber which is typically defined by a body extension. A valve mechanism is located between the body chamber and access chamber and is capable of establishing a seal therebetween in order that the access chamber may be depressurized and opened without depressurizing the flow line. With the body chamber seal in place, the access chamber is depressurized in order to allow removal of an orifice plate from the framework and installation of a replacement orifice plate therein.
Typically, several external operating handles are employed which drive internal gears that function in concert to shift the orifice plate framework between the body chamber and the access chamber. Of course, this is accomplished with the body chamber valve in its open condition and with the access chamber in its closed and sealed condition. Since the orifice plate framework is encapsulated either within the body chamber or access chamber during manipulation of the framework, it is frequently difficult for service personnel to determine its proper location and to manipulate the multiple external handles so as to accomplish positioning of the framework within the body chamber for use and within the access chamber for installation and removal of the orifice plate. It is desirable therefore to provide an orifice plate mechanism having the capability of achieving proper positioning of the orifice plate through manipulation of a single orifice plate actuator. It is also desirable to provide an orifice plate mechanism wherein simple orifice plates may be utilized efficiently without the requirement to provide expensive frameworks within which the orifice plate is secured for use.